Why do u think the mountaineers carry oxygen cylinders with them while climbing mountain ?
Kindly refer to the following link
https://www.meritnation.com/ask-answer/question/why-do-mountaineers-carry-oxygen-cylinders-with-them/air-around-us/3088014
https://www.meritnation.com/ask-answer/question/why-do-mountaineers-carry-oxygen-cylinders-with-them/air-around-us/3088014